The no ip domain-lookup is very useful, what this command does is tell the Cisco device not to do a domain lookup when you mistype something in the CLI. For example if you do this without the no ip domain-lookup:

The Cisco device will try to find the computer name of pign, it doesn't know that you mistyped ping. This process could take a very long time.If you apply the no ip domain-lookup, the Cisco device won't try to do the domain lookup.

The second command is the alias command. This command makes an alias of a command that you use frequently.For example you often use the command show ip interface brief, you can make an alias of it to be "ship".

router (config)# alias exec ship show ip interface brief

You configure it by entering alias first, followed by which mode the command resides in - in this example the show command resides in the exec mode - type in the alias for the command, then you enter the full commands that you want to make alias.Now you just have to type in ship instead of the long show ip interface brief command.

Next command is useful when you connect to the Cisco devices and you need a very long time to configure it.The Cisco devices have a default time of how long you're allowed to get connected to them. Sometimes you don't want to reconnect again all the time, but mind you that the time limitation is set because of security concern.

router (config)# line vty 0 4router (config-line)# no exec-timeout

The above commands tell the router to give you all the time that you need when configuring the router from the telnet session, it won't cut your connection. You can also configure it for the console connection.

Last one is my favorite one, you know when you're configuring a Cisco device sometimes you'd get some notifications from the device which is great, it tells you things going on in it.But it gets annoying when you're trying to configure it and the notifications just cut down your halfway written command.The following command tells the router to write back the command you entered before the notifications cut it: